StyroCrete vs. Rastra
Okay, folks, I found the info. on Rastra: it's an ICF, an
Insulated Concrete Form.
What it is:
An ICF, (of which Rastra is one of numerous competing brands, each
slightly different), is a system of interlocking polystyrene foam
blocks with vertical holes like GreenStar Blox, and horizontal
grooves, top and bottom, all of which accept steel rebar running both
directions. Dimensions typically match commercial cinderblocks. A
foundation is prepared with vertically protruding steel rebar where
the vertical holes in the walls will be. A course of blocks, one
single layer, is laid. Horizontal rebar is laid in the top groove of
this. Another layer, more horizontal rebar. Repeat. As it gets
higher, maybe drop in vertical rebar that would have been
inconveniently tall if used initially. When desired wall height is
reached, the structure is braced from both sides so that it cannot
tilt, all alignments are checked, and then concrete is poured in
through all of the holes on top. You now have a
styrofoam-encapsulated grid of steel reinforced concrete. It is
amazingly strong, thermally R-20 to R-50, non-biodegradable, nearly
indestructible. You probably had the foresight to include little
sheet metal tabs between the blocks that give anchor points to attach
fascia and drywall. Both Styrocrete and Polysteel are names of
existing ICF brands, and the name StyroCrete has also been used for a
concrete coating used for expanded polystyrene.
That, in a nutshell, is the ICF system. It is considered "green"
because it produces well-insulated structures and consumes recycled #6
polystyrene waste, a non-biodegradable dead end of our civilization.
Now you see why Rastra is 85% foam by volume, when such levels,
shredded and mixed into foamcrete homogenously, might be disastrous.
If I were to have built a "custom round home with a geodesic
truss roof," (the building code euphemism for a Wil Fidroeff Dome
Home), ICF construction would have been my choice for the decagon
basement and riser wall.
Drawbacks: Whatever you do, you'd better be right, because the
resulting monolithic structure is pretty much immune to alteration,
(imagine attempting a room addition or repairing a leaky pipe?). If I
were building this way, I'd include 3" or 4" FOTM conduit, (Flavor of
the Month), so that I could add Monster Cable, fiber optic or holonet
lines later. I guess if there's one thing I don't like about ICF it's
the _permanence_. I'd rather get xBlox with added grooves top and
bottom, use cable or smooth steel rod instead of rebar, and then
tension the rods after assembly. In concrete, post-tensioning adds
strength. What will it do in papercrete? Will it get things to seal
well enough that no mortar or other sealants are required? Or will
long, horizontal runs mean that when those rods are tightened, the
whole wall gets wavy? (And the waviness would not spell doom; it
would just dictate the spacing of hollow, square steel pillars to
house the rod ends and fasteners). That's why engineers want the
data. With concrete, they know they can cast the stuff, post-tension
the steel, then park cars in it. Once you decide you're done with the
xBlox structure, you can remove the nuts, washers, planks or plates,
and _sell_ the xBlox for reuse by others elsewhere. Reuse the parts
and recover the use of the land! Now _that's_ Green!
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